Question

# A fish rising vertically up towards the surface of water with speed 3 observes a bird diving vertically down towards it with speed 9 . The actual velocity of bird is

- 4.5
- 5.
- 3.0
- 3.4

## The correct answer is: 4.5

### Here optical distance between fish and the bird is

Differentiating *w.r.t t* we get

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We can only apply the L’Hospital’s rule if the direct substitution returns an indeterminate form, that means

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If , then by trapezoidal rule is

If , then by trapezoidal rule is

We can only apply the L’Hospital’s rule if the direct substitution returns an indeterminate form, that means